Most conventional detergent compositions contain mixtures of various detersive surfactants in order to remove a wide variety of soils and stains from surfaces. For example, various anionic surfactants, especially the alkyl benzene sulfonates, are useful for removing particulate soils, and various nonionic surfactants, such as the alkyl ethoxylates and alkylphenol ethoxylates, are useful for removing greasy soils. While a review of the literature would seem to suggest that a wide selection of surfactants is available to the detergent manufacturer, the reality is that many such materials are specialty chemicals which are not suitable for routine use in low unit cost items such as home laundering compositions. The fact remains that many home-use laundry detergents still comprise one or more of the conventional alkyl benzene sulfonate or primary alkyl sulfate surfactants.
One class of surfactants which has found limited use in various compositions where emulsification is desired comprises the secondary alkyl sulfates. The conventional secondary alkyl sulfates are available as generally pasty, random mixtures of sulfated linear and/or partially branched alkanes. Such materials have not come into widespread use in laundry detergents, since they offer no particular advantages over the alkyl benzene sulfonates.
Modern granular laundry detergents are being formulated in "condensed" form which offers substantial advantages, both to the consumer and to the manufacturer. For the consumer, the smaller package size attendant with condensed products provides ease-of-handling and storage. For the manufacturer, unit storage costs, shipping costs and packaging costs are lowered.
The manufacture of acceptable condensed granular detergents is not without its difficulties. In a typical condensed formulation, the so-called "inert" ingredients such as sodium sulfate are mainly deleted. However, such ingredients do play a role in enhancing the solubility of conventional spray-dried detergent; hence, the condensed form will often suffer from solubility problems. Moreover, conventional low-density detergent granules are usually prepared by spray-drying processes which result in porous detergent particles that are quite amenable to being solubilized in aqueous laundry liquors. By contrast, condensed formulations will typically comprise substantially less porous, high density detergent particles which are less amenable to solubilization. Overall, since the condensed form of granular detergents typically comprises particles which contain high levels of detersive ingredients with little room for solubilizing agents, and since such particles are intentionally manufactured at high bulk densities, the net result can be a substantial problem with regard to in-use solubility.
It has now been discovered that a particular sub-set of the class of secondary alkyl sulfates, referred to herein as secondary (2,3) alkyl sulfates ("SAS"), offers considerable advantages to the formulator and user of detergent compositions. For example, the secondary (2,3) alkyl sulfates are available as dry, particulate solids. Accordingly, they prospectively can be formulated as high-surfactant (i.e., "high-active") particles for use in granular laundry detergents. Since, with proper care in manufacturing, the secondary (2,3) alkyl sulfates are available in solid, particulate form, they can be dry-mixed into granular detergent compositions without the need for passage through spray drying towers. In addition to the foregoing advantages seen for the secondary (2,3) alkyl sulfates, it has now been determined that they are both aerobically and anaerobically degradable, which assists in their disposal in the environment. Desirably, the secondary (2,3) alkyl sulfates are quite compatible with detersive enzymes, especially in the presence of calcium ions.
Unfortunately, commercially available SAS particles are somewhat deficient with regard to their rate of solubility in cooler aqueous wash liquors. This problem is especially acute in countries where consumers prefer cold washing temperatures, i.e., as low as about 5.degree. C. This problem is further exacerbated when SAS is used in high density detergent granules.
The present invention converts commercial SAS powder which has a relatively slow dissolution rate into fast-dissolving detergent particles. Importantly, the SAS particles provided herein are free-flowing, and can be readily admixed with other ingredients to provide fully-formulated granular detergents. Accordingly, the present invention overcomes many of the problems associated with the use of SAS in granular laundry detergents or other granular cleaning compositions.